Manage one object inside list of object java

I have List of object that list of object is shown same object multiple time but only color field different for all duplicate object. I want to change response.

if anyone have solution for this create common method and pass this list and covert into as per my expectation response.

1.Actual Response

[
{
"id": 21,
"startDate": "2020-07-21",
"startTime": "10:28:34+05:30",
"endDate": "2020-07-21",
"endTime": "19:28:34+05:30",
"eventName": "Stretegic Planing for Business Success",
"location": "America Phoenix",
"city": "San Jose de Gracia",
"eventImg": "Image Url",
"passport": false,
"passportDiscountPercent": 5,
"featured": true,
"myFavourite": true,
"color": "Yellow"
},
{
"id": 21,
"startDate": "2020-07-21",
"startTime": "10:28:34+05:30",
"endDate": "2020-07-21",
"endTime": "19:28:34+05:30",
"eventName": "Stretegic Planing for Business Success",
"location": "America Phoenix",
"city": "San Jose de Gracia",
"eventImg": "Image Url",
"passport": false,
"passportDiscountPercent": 5,
"featured": true,
"myFavourite": true,
"color": "Green"
},
{
"id": 76,
"startDate": "2020-07-21",
"startTime": "10:28:34+05:30",
"endDate": "2020-07-21",
"endTime": "19:28:34+05:30",
"eventName": "Stretegic Planing for Business Success",
"location": "string",
"city": "Villa Juarez",
"eventImg": "Imgage url",
"passport": false,
"passportDiscountPercent": 5,
"featured": false,
"myFavourite": true,
"color": "Red"
},
{
"id": 76,
"startDate": "2020-07-21",
"startTime": "10:28:34+05:30",
"endDate": "2020-07-21",
"endTime": "19:28:34+05:30",
"eventName": "Stretegic Planing for Business Success",
"location": "string",
"city": "Villa Juarez",
"eventImg": "Imgage url",
"passport": false,
"passportDiscountPercent": 5,
"featured": false,
"myFavourite": true,
"color": "Black"
}
]    

2.Expect Response

[
{
"id": 21,
"startDate": "2020-07-21",
"startTime": "10:28:34+05:30",
"endDate": "2020-07-21",
"endTime": "19:28:34+05:30",
"eventName": "Stretegic Planing for Business Success",
"location": "America Phoenix",
"city": "San Jose de Gracia",
"eventImg": "Image Url",
"passport": false,
"passportDiscountPercent": 5,
"featured": true,
"myFavourite": true,
"eventType": [
{
"color": "Yellow"
},
{
"color": "Green"
}
]
},
{
"id": 76,
"startDate": "2020-07-21",
"startTime": "10:28:34+05:30",
"endDate": "2020-07-21",
"endTime": "19:28:34+05:30",
"eventName": "Stretegic Planing for Business Success",
"location": "string",
"city": "Villa Juarez",
"eventImg": "Imgage url",
"passport": false,
"passportDiscountPercent": 5,
"featured": false,
"myFavourite": true,
"eventType": [
{
"color": "Red"
},
{
"color": "Black"
}
]
}   
]    

Step 1: Create Schema Classes

Initial Response Model:

public class InitialModel {
String id;
String color;
}

Final/Converted Response Model:

public class Model {
String id;
List<Color> eventType = new ArrayList<>();
class Color {
String color;
public Color(String color) {
this.color = color;
}
}
}

Step 2: Iterate initial response and convert it to the final response

List<Model> modelList = new ArrayList<>();
List<InitialModel> initialModelList = new Gson().fromJson(jsonString, new TypeToken<List<Model>>(){}.getType());
for (InitialModel initialModel : initialModelList) {
Model tempModel = null;
// Check if model with same id already exists
for(Model model : modelList){
if(initialModel.id.equals(model.id)){
tempModel = model;
break;
}
}
// Create new model if id doesn't exists
if(tempModel==null) {
tempModel = new Model();
tempModel.id = initialModel.id;
modelList.add(tempModel);
}
tempModel.eventType.add(new Color(initialModel.color));
}

Result Json:

String resultJson = new Gson().toJson(modelList);

1.I have add your code but some error is getting

private List<EventCustomDTO> commonListView(List<EventDtoClass> eventDtoClassList) {
List<EventCustomDTO> eventCustomDTOList = new ArrayList<>();
List<EventDtoClass> eventDtoClasses = new Gson().fromJson(eventDtoClassList.toString(), new TypeToken<List<EventCustomDTO>>(){}.getType());
for (EventDtoClass eventDtoClass : eventDtoClasses) {
EventCustomDTO eventCustomDTO = null;
for(EventCustomDTO model : eventCustomDTOList){
if(eventDtoClass.getId().equals(model.getId())){
eventCustomDTO = model;
break;
}
}
if(eventCustomDTO == null) {
eventCustomDTO = new EventCustomDTO();
eventCustomDTO.getId() = eventDtoClass.getId();
eventCustomDTOList.add(eventCustomDTO);
}
eventCustomDTO.getEventType().add(new TypesOfEvents(eventDtoClass.getEvenTypeId(),eventDtoClass.getColor()));
}
return eventCustomDTOList;
}

Since you have different JSON in your expected result you will need to have 2 classes to serialize/deserialize from. Lets consider following classes:

@Getter
@AllArgsConstructor
private class ObjectA {
public Long id;
public String color;
}
@ToString
@AllArgsConstructor
private class ObjectB {
public Long id;
public String eventType;
}

Now the code to obtain your expected result in this case would be something like this:

List<ObjectA> object = List.of(new ObjectA(1L, "green"), new ObjectA(1L, "red"), new ObjectA(2L, "yellow"));
object.stream().collect(Collectors.groupingBy(ObjectA::getId))
.entrySet() // from map of grouped ObjectA's
.stream()
.map(entry -> new ObjectB(entry.getKey(), // GroupID
entry.getValue() // list of grouped ObjectA's by current GroupID
.stream()
.map(ObjectA::getColor) // change to stream of all color strings from grouped ObjectA's by current GroupID
.collect(Collectors.joining(", ")))
).forEach(System.out::println);
//.collect(Collectors.toList());

With output:

ObjectB(id=1, eventType=green, red)
ObjectB(id=2, eventType=yellow)

You can adjust that code simply for your use case.